$-5ln - 5m + 5n + 1 = 9m + 2n + 9$ Solve for $l$.
Solution: Combine constant terms on the right. $-5ln - 5m + 5n + {1} = 9m + 2n + {9}$ $-5ln - 5m + 5n = 9m + 2n + {8}$ Combine $n$ terms on the right. $-5ln - 5m + {5n} = 9m + {2n} + 8$ $-5ln - 5m = 9m - {3n} + 8$ Combine $m$ terms on the right. $-5ln - {5m} = {9m} - 3n + 8$ $-5ln = {14m} - 3n + 8$ Isolate $l$ $-{5}l{n} = 14m - 3n + 8$ $l = \dfrac{ 14m - 3n + 8 }{ -{5n} }$ Swap the signs so the denominator isn't negative. $l = \dfrac{ -{14}m + {3}n - {8} }{ {5n} }$